1. FIELD OF THE INVENTION
This invention relates in general to the construction of transport ships and in particular to a new and useful transport ship for handling floating cargo and to an improved method of loading the floating cargo.
2. DESCRIPTION OF THE PRIOR ART
Transport ships for carrying floating cargo are known and are referred to as lash ships and as barge carriers. The loading and discharging of floating containers or vessels with such ships is as a rule done on free water by shipborne lifting devices which pick up the floating vessels from the water for transfer to the ship and vice versa. Such expensive shipborne lifting devices have the common disadvantage that they require an assembly of a large number of individual parts with a relatively low degree of reliability and in most cases the loading and unloading operations are impaired by the sea water conditions and the atmospheric environment of the ship. A further disadvantage is that such vessels usually have to be operated by shore side personnel because of the prevailing agreements between ship owners and longshoremen unions. Such personnel are normally unable to operate such gear as carefully and safely as a trained crew of the ship. In addition with the use of travelling ship cranes for the handling of floating vessels, the cranes sensitivity to the ship's inclination is a further disadvantage.
So-called float in and float off ships are also known in which the floating cargo is floated into the ship's cargo space in superposed tiers in order to avoid the disadvantages of the use of ship borne lifting devices. A disadvantage of this arrangement is however that the ship must be lowered for each tier to an immersion of the ship which allows the floating vessels to be stowed into a stowage level vertically fixed within the ship. In addition they must be adjusted to fix deck or girder structures which segregate the cargo containers at various cargo levels. With such ships the height of the stowage spaces for each tier of floating cargo or floating containers has to be increased beyond and above the height of the floating vessels by an amount which results from the height differential between the light and deep load line of the floating vessels from the upper and lower safety margin in order to allow an undisturbed and accident free float in an float off of the vessels and from the requisite height to accommodate the structures of the ship which segregate the cargo levels. This results in the creation of a dead space in each cargo level above each settled tier of floating vessels and this requires that the depth of the transport ship be increased by this height differential for each tier of the floating vessels. The increased depth of the ship results in an increased ship's weight. This also requires that the ship's beam to be increased in order to maintain sufficient stability against capsizing of the ship. The increased beam again results in further increased ship's weight and all of this additional weight requires additional propulsive power. Therefore, the known ships of this type become more expensive in construction as well as in operation.
The water depth requisite to accommodate such a ship when docking or releasing the floating vessels increases with the ship's depth. Thus, this limits the employment possibilities or prohibits the employment of such a ship precisely where the cargo loading and discharging has to be carried out that is in the coastal waters and as a rule restricts the use of the ships in respect to the depth of such waters.